The present invention is in the field of battery technology and, more particularly, in the area of high-energy materials for use in electrodes in electrochemical cells.
Cathodes formed from active materials of the composition LiM2O4 are a common class of active materials in lithium ion batteries, where M includes a transition metal. The LiM2O4 active material can have a spinel structure. Transition metals such as manganese have been used as the transition metal in LiM2O4 active materials and, in some instances, both manganese and nickel have been used.
LiM2O4 active materials have been studied and characterized. While they are relatively stable and have relatively low synthesis and raw materials costs, they are not an ideal material. For the sake of comparison, a LiMn2O4 active material has a theoretical gravimetric energy density of about 492 Wh/kg and a LiMn1.5Ni0.5O4 has a theoretical gravimetric energy density of about 691 Wh/kg. Other cathode active materials, such as layered oxide materials, have higher theoretical energy densities. In particular, layered oxides that have been over-lithiated (that is, additional lithium is inserted into the layered oxide structure) can have a theoretical gravimetric energy density of about 1110 Wh/kg.
However, over-lithiated layered oxides (OLO) have some disadvantages, including up to 30% irreversible capacity loss, gas generation on the first cycle, and poor rate capability. Another factor limiting their use is the voltage suppression on cycling due to gradual structure change.
Some work has been done to incorporate additional lithium into LiM2O4 active materials to improve their energy density. The spinel structure of LiM2O4 can accommodate more lithium. By adding one lithium to LiM2O4, the phase Li2M2O4 is obtained, which has a theoretical gravimetric energy density of about 1087 Wh/kg. An over-lithiated LiM2O4 active material may have a lower raw material cost compared to other materials with similar energy density, such as OLO materials. However, the voltage at which this additional lithium is removed from the structure during discharge of the battery is below three volts, which is too low to be of practical use.
These and other challenges can be addressed by certain embodiments of the invention described herein.